The long-term objective of this application is the prevention of the humoral rejection of porcine xenografts in patients. The objective of the current proposal is a detailed characterization of the xenoantibody response of an experimental model for human xenotransplantation, the cynomolgus monkey, and validation of this model as the basis for conducting clinically relevant experiments to prevent xenograft rejection in humans. In pursuit of this objective, our specific aims include determining the binding characteristics of IgM and IgG xenoantibodies in the cynomolgus monkey, and the sequences of the VH genes encoding them, both before and after transplantation of a vascularized porcine graft. Once this genetic information has been obtained, it will be used in the development and in vitro testing of an anti-idiotypic antibody against those xenoantibodies with the highest affinity to identified xenoantigens. This research should result in the full characterization of the xenoantibody response of an experimental model for human xenotransplantation and validation of this model as the basis for conducting clinically relevant experiments to prevent xenograft rejection in humans. Dr. Joanne Zahorsky-Reeves will be working under her mentor, Dr. Donald V. Cramer, in a laboratory with extensive background in the xenoantibody response in both rodent and human models. The applicant will become proficient in a variety of molecular biology techniques, including the development and screening of genetic libraries; the creation of single-chain antibodies; the production of anti-idiotypic antibodies using a mouse hybridoma system; and the evaluation of those anti-idiotypic Antibodies to specifically target and eliminate antibody- producing B cells. Mastering of these techniques will allow Dr. Zahorsky-Reeves to become an independent animal-based research not only in the field of xenotransplantation, but, broadly, in a variety of immunological settings.